Study on the Meso-Energy Damage Evolution Mechanism of Single-Joint Sandstone under Uniaxial and Biaxial Compression

Energy conversion and release occur through the entire deformation and failure process in jointed rock masses, and the accumulation and dissipation of rock mass energy in engineering can reveal the entire process of deformation and instability. This study uses PFC2D to carry out numerical simulation tests on single-joint sandstone under uniaxial compression and biaxial compression, respectively, and analyse the influence of joint inclination, length, and confining pressure on the meso-energy conversion process and phase evolution of jointed sandstone. Through analysis, it is found that the input meso total strain energy is transformed into meso dissipated energy and meso-elastic strain energy. Macroscopic and microscopic joint sandstone law is consistent with the overall energy evolution; and the difference is reflected in two aspects: (1) the microlevel energy evolution has no initial compaction energy consumption section and (2) the linear energy storage section before the macroenergy evolution peak can be subdivided into two sections in the meso-level energy evolution. Under uniaxial compression, the energy values at the characteristic points of the meso-level energy evolution phases first asymmetrically decrease and then increase with the increase of the joint inclination. The initiation point of jointed sandstone is significantly affected by the length of the joint, and the degradation effect of the meso-energy at the damage point and peak point weakens with the increase of the joint length. Comparing the data obtained from the PFC numerical simulation with the experimental data, it is found that the error is small, which shows the feasibility of the numerical model in this paper. Under biaxial compression, the accumulation rate of meso-elastic strain at the peak point of the jointed sandstone first decreases and then increases with the joint inclination angle. After the peak of jointed sandstone, the rate of sudden change of meso-energy change decreases with the increase of joint length. The conditions of high confining pressure will promote the meso-accumulated damage degree of the jointed sandstone before the peak, while inhibiting the meso-energy and the mutation degree of the damage after the peak. The higher the confining pressure, the more obvious the joint length and inclination effect characteristics of the elastic strain energy at the peak point of the jointed sandstone.

Failure of Rock Slopes With Intermittent Joints: Failure Process and Stability Calculation Models

Rock slopes with intermittent joints in open-pit mines are complex geological bodies composed of intact rock and discontinuous structural planes, and their stability analysis are necessary for mine disaster prevention. In this study, a series of base friction tests were performed to determine the failure process and displacement field evolution of rock slopes with intermittent joints using the speckle technique of a noncontact measurement system. Next, stability calculation models of the slopes were established from the energy perspective using the plastic limit analysis theory, and the effects of the joint inclination angle and coalescence coefficient of rock bridges on the slope stability were evaluated. The four main conclusions are as follows. (1) The failure of rock slopes with intermittent joints shows the feature of collapse-lower traction-upper push. (2) Based on the failure modes of rock bridges in slopes, the failure of rock slopes with intermittent joints could be divided into three types: tensile coalescence (Type A), shear coalescence (Type B), and tensile–shear coalescence (Type C). (3) Among the three slope types, the stability of the Type A slope is significantly influenced by rock cohesion, whereas that the Type B slope is significantly influenced by joint cohesion. The stability of the Type C slope is significantly influenced by the joint inclination angle and joint friction angle. (4) The local-stable slope is unstable while the first through-tensile crack in the zone of the potential sliding body higher than the critical instability height appeared. This study guides the stability evaluation and instability prediction of jointed rock slopes in open-pit mines.

Restoration of Joint Inclination in Total Knee Arthroplasty Offers Little Improvement in Joint Kinematics in Neutrally Aligned Extremities

Kinematically aligned total knee replacements have been shown to better restore physiological kinematics than mechanical alignment and also offer good postoperative satisfaction. The purpose of this study is to evaluate the extent to which an inclined joint line in a kinematically aligned knee can alter the postoperative kinematics. A multi-body dynamic simulation was used to identify kinematic changes in the joint. To accurately compare mechanical alignment, kinematic alignment and a natural knee, a “standard” patient with neutral alignment of the lower extremities was selected for modeling from a joint database. The arthroplasty models in this study were implanted with a single conventional cruciate-retaining prosthesis. Each model was subjected to a flexion movement and the anteroposterior translation of the femoral condyles was collected for kinematic analysis. The results showed that the mechanical alignment model underwent typical paradoxical anterior translation of the femoral condyles. Incorporating an inclined joint line in the model did not prevent the paradoxical anterior translation, but a 3° varus joint line in the kinematic alignment model could reduce the peak value of this motion by about 1 mm. Moreover, the inclined joint line did not restore the motion curve back to within the range of the kinematic curve of the natural knee. The results of this study suggest that an inclined joint line, as in the kinematic alignment model, can slightly suppress paradoxical anterior translation of the femoral condyles, but cannot restore kinematic motions similar to the physiological knee. This finding implies that prostheses intended to be used for kinematic alignment should be designed to optimize knee kinematics with the intention of restoring a physiological motion curve.

Research on crack evolution law and macroscopic failure mode of joint Phyllite under uniaxial compression

In order to explore the fracture mechanism of jointed Phyllite, the TAJW-2000 rock mechanics test system is used to carry out uniaxial compression tests on different joint inclination Phyllites. The influence of joint inclination of Phyllite failure mode is discussed, and the progressive failure process of Phyllite is studied. The test results show that the uniaxial compressive strength anisotropy of jointed Phyllite is remarkable. As the inclination increases, it exhibits a U-shaped change; When 30° ≤ α ≤ 75°, the tensile and shear failures along the joint inclination mainly occurs. the joint inclination controls the failure surface form of the Phyllite; The crack initial stress level of the joint Phyllite is 0.30–0.59σf, the crack failure stress level is 0.44–0.86σf. When α = 90°, the σcd value is the largest, and σcd with α = 90° can be used as the maximum reliable value of uniaxial compressive strength of Phyllite. Using the theory of fracture mechanics, it is analyzed that under uniaxial compression of the rock, the crack does not break along the original crack direction, but extends along the direction at a certain angle to the original crack. The joint effect coefficient is proposed to show the influence of the joint inclination on the uniaxial compressive strength of the phyllite. Both the test and simulation results show that when the joint inclination is 60°, the joint effect coefficient is the largest. The compressive strength is the smallest. Numerical simulation analyses the crack evolution law of phyllite under different joint inclination under uniaxial compression, which verifies that there are different failure modes of joint phyllite under uniaxial compression.

Effects of 24-Epibrassinolide, Bikinin, and Brassinazole on Barley Growth under Salinity Stress Are Genotype- and Dose-Dependent

Brassinosteroids (BRs) are involved in the regulation of many plant developmental processes and stress responses. In the presented study, we found a link between plant growth under salinity stress and sensitivity to 24-epibrassinolide (24-EBL, the most active phytohormone belonging to BRs), brassinazole (Brz) and bikinin (inhibitors of BR biosynthesis and signaling pathways, respectively). Plant sensitivity to treatment with active substances and salinity stress was genotype-dependent. Cv. Haruna Nijo was more responsive during the lamina joint inclination test, and improved shoot and root growth at lower concentrations of 24-EBL and bikinin under salinity stress, while cv. Golden Promise responded only to treatments of higher concentration. The use of Brz resulted in significant dose-dependent growth inhibition, greater for cv. Haruna Nijo. The results indicated that BR biosynthesis and/or signaling pathways take part in acclimation mechanisms, however, the regulation is complex and depends on internal (genotypic and tissue/organ sensitivity) and external factors (stress). Our results also confirmed that the lamina joint inclination test is a useful tool to define plant sensitivity to BRs, and to BR-dependent salinity stress. The test can be applied to manipulate the growth and stress responses of crops in agricultural practice or to select plants that are sensitive/tolerant to salinity stress in the plant breeding projects.

Acoustic Emission Characteristics and Joint Nonlinear Mechanical Response of Rock Masses under Uniaxial Compression

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainly involved three stages: (I) the closing of the joint; (II) the strength mobilization of the joint; and (III) the reopening of the joint. Moreover, the response of the pre-existing joint was closely related to the joint’s inclination. As the joint inclination angle increased, the strength mobilization stage of the joint gradually shifted from the pre-peak stage of the stress–strain curve to the post-peak stage. In addition, the instantaneous drop in the average joint system aperture (aave) in the specimens with medium and high inclination angles corresponded to a rapid increase in the form of the pulse of the AE activity during the strength mobilization stage.

Numerical Study on Anisotropic Influence of Joint Spacing on Mechanical Behavior of Rock Mass Models under Uniaxial Compression

Mechanical properties of rock masses are dominated by the nonlinear response of joints and their arrangement. In this paper, combined influences of joint spacing (s) and joint inclination angle (β) on mechanical behavior of rock mass models with large open joints under uniaxial compression were investigated by PFC modeling. With a large amount of local measurement circles placed along the pre-defined measurement lines (ML), stresses and joint response parameters at different scales (the measurement circles, the MLs and the whole specimen) were defined and calculated. It was found that macroscopic behaviors of the jointed specimens, such as four types of deformation behaviors, four failure modes, strength, deformability modulus and ductility index, are dominated by nonlinear response of the joint system, especially the interaction between the joints and rock bridges. The joints may experience three stages, i.e., starting to close, closed and opening again. On the joint plane, the peak stresses of the rock bridges and those of the joints may not be reached at the same time; i.e., joint strength mobilization happens with the loss of the rock bridges’ resistance. The influence of s on specimen behavior is little for β = 90°, obvious for β = 0° or 30° and significant for β = 45° or 60°, and this can be related to their different microscopic damage mechanisms.

Association Between the Morphology of Proximal Tibiofibular Joint and the Presence of Knee OA

Objective: The aim of this study was to evaluate the association between the morphology of the proximal tibiofibular joint (PTFJ) and the presence of knee osteoarthritis (OA).Methods: Twenty-eight OA subjects and 30 healthy subjects were enrolled in this study. A 3D model of the lower limb of each subject was constructed from CT scans and used to measure the characteristics of the PTFJ, including the shape of the articular facets, articular surface area, joint inclination, relative articular height, and joint declination. The association between the characteristics of the PTFJ and presence of knee OA was assessed using binomial logistic regression analysis.Results: There was a significant difference between the OA and healthy groups in terms of the inclination (p = 0.028) and declination (p = 0.020) of the PTFJ and relative articular height (p = 0.011). A greater inclination angle (OR: 1.463, 95% CI: 1.124–1.582, p = 0.021), greater declination angle (OR: 1.832, 95% CI: 1.691–2.187, p = 0.009), and lower relative articular height (OR: 0.951, 95% CI: 0.826–0.992, p = 0.008) were found to be associated with an increased likelihood of knee OA being present.Conclusion: The results of this study suggest that abnormal PTFJ morphology is associated with the presence of knee OA.